The invention relates generally to systems and methods for cleansing harbors and more particularly to such systems and methods which utilize the forces produced by the tides to flush water through the harbor and thereby remove therefrom harbor contaminants which are suspended or dissolved in the harbor waters or which may be simply carried away by the forces of the water currents. The invention is particularly useful in harbors which do not have a river stream emptying thereinto and which therefore do not have a natural flushing system to cleanse the harbor.
Harbors without a river must rely instead on ocean tide action for cleaning. The effectiveness of the tide in replenishing polluted water is diminished by the absence of any inherent flow of water associated with the tide. In that sense the tide is similar to wind driven waves which manifest only minor flow of water. This minor actual water flow renders the un-modified tide action a poor general cleaning instrument.
Water movement near the harbor inlet moves in and out from the ocean and thus replenishes the inlet with clean water from the ocean. This therefore results in effective cleaning. However, the water substantially inside the inlet is not connected directly with ocean water. This water therefore tends to slosh aimlessly back and forth with the tide without yielding effective cleaning. The waters in the inner areas of the harbor are thus generally stagnant and pollutants consequently tend to accumulate unabated in these areas.
This invention utilizes the natural characteristics of the tide to establish and maintain clean water circulation throughout the entire harbor. This circulation bring clean water directly to the inner harbor, or back harbor, to replace stagnant water.
Consider the phenomenon that is the tide. The tide is caused primarily by cyclic forces provided by the gravitational pull of the moon on the ocean waters. In response to these gravitational forces the water surface seeks to follow the relative position of the moon with respect to the earth. However, the actual forward propagation velocity of the elevation changes is modified by the free velocity of propagation in water in response to external disturbances. This free velocity constitute the propagation velocity of the tide. It is equal to the square root of the product of the acceleration of gravity and the depth of the water.
The combination of cyclic gravitational forces with the free velocity of propagation combine to give the tide a natural, wave-like nature. Thus the tide propagates in the form of a series of crests and troughs similar to wind-driven waves. The wavelength, the distance from crest to crest, of the tide wave is determined by the propagation velocity in water and the lunar period according to well understood physical principles.
The change of surface elevation along the path of propagation resulting from the wave tide wave is a fundamental characteristic of tide behavior. This characteristic provides the fundamental underlying principle supporting this invention. These elevation changes result in corresponding hydrostatic pressure changes in the water along the path of propagation of the tide. A comparison of hydrostatic pressure between diverse points along the path produces a hydrostatic pressure differential, or head.
The instant invention relies on the natural head between points along the path of propagation and implements the invention by connecting a submerged pipe from one point along the propagation path to another. For example, if the pipe connects a tide crest with a through, then water will flow according to well understood hydraulic principles of flow of fluids.
The principle is completely general. Therefore, the invention as described would theoretically function equally well in an open ocean. It needs no artificial abstruction to generate a head; the generated hydraulic head is inherent in the propagation of the tide itself.
In practical terms the wavelength in an open ocean, measured in hundreds of miles, is prohibitively long to implement the invention there. However, in a small boat harbor, or in a wetlands area or bay, the water depths are such that the wavelengths are measured in miles or fractions of miles instead of hundreds of miles. This makes the invention entirely feasible in such a harbor. Therefore the applicant's invention does not need any dam means or artificially created constrictions which impedes shipping in a harbor for the purpose of generating a head.
Some prior art systems use the energy of water currents or waves to cleanse a harbor. An example of such a device is dislcosed in U.S. Pat. No. 833,543 to Parker. The Parker device uses the force of impact or dash of waves against a floating apron. The apron floats so that the top of the apron lies int he water surface. The waves, upon impact, splashes over the top of the apron and into a connecting reservoir behind the apron. The level of water in the reservoir consequently rises to produce a head that is at a wave-determined differential height relative to the sea level at a particular time. This differential head is used to effect flow of fresh sea water into the bay via a connective canal.
The apron of the Parker patent floats with the surface of the ocean water. It therefore also floats with the tide. Consequently, the reservoir behind the apron is independent of the tide. Thus, the Parker invention does not utilize the tide as a head producing agent.
The problem with the Parker patent is that it ignores the effects of tide variances within the bay. This may in fact render the method inoperable as the tide in the bay may be higher than the wave generated head of water.
Other types of prior art devices for cleansing harbors utilize reservoirs to collect waters moved by tidal flow. An example of such a device is disclosed in U.S. Pat. No. 4,162,864 to Maeda. The Maeda device uses one or more reservoirs to collect water brought therein by the tides.
Floodgates are also provided to control water flow into and out of the reservoirs. Appropriate floodgates are opened to release water from the reservoirs into the harbor when the reservoir waters have a head higher than the sea and when the tide has begun to ebb. However, a primary disadvantage with such a system is that construction of such reservoirs may be unreasonably expensive and operation and maintenance of the floodgates may also be inordinately expensive. In addition, the large size and number of the reservoirs take up valuable space in the harbor and may also interfere with normal usage of the harbor.
A harbor cleansing system is thus needed which can effectively flush water from stagnant (or dead water) areas of a harbor. A harbor cleansing system is also needed that is economical and neither requires a lot of harbor space nor interferes with normal harbor usage.